Basically I've built a simple circuit that outputs a square wave of different frequencies (i.e. a DIY tone generator), but it obviously sounds very robotic. Are there any small, simple devices that could take an input of a certain frequency and output something that sounds more like an instrument? Like a single note played on a piano or a bell corresponding to the frequency input. This is just a simple DIY side project so I'm trying not to have anything too large or expensive.
I know very little about electronic sound generation so sorry if this has an obvious answer; I haven't been able to find anything through google.